The present invention relates to a motor-driven compressor.
As one of the global warming prevention measures, in the refrigerant circuit of a vehicle air-conditioner, new type refrigerant having little effect on ozone depletion has been replacing conventional refrigerant such as chlorofluorocarbon. A refrigerant whose molecular formula is C3HmFn (wherein “m” is an integer from one to five, “n” is an integer from one to five, and an equation of “m+n=6” is satisfied) and which has one double bond, such as CF3—CF═CH2 (2,3,3,3-tetrafluoro-1-propene) as disclosed in Japanese Patent Application Publication No. 2009-225636, has recently been attracting the attention of the industry as a new type refrigerant (hereinafter referred to as “HFO1234yf type refrigerant”).
HFO1234yf type refrigerant which has the double bond tends to be decomposed in the presence of moisture. If moisture enters into the refrigerant circuit for some reason during manufacturing or use of a vehicle air-conditioner having HFO1234yf type refrigerant, the refrigerant is decomposed and, accordingly, hydrogen fluoride (HF) is produced from fluorine (F) in the refrigerant. Acid such as HF causes early corrosion to metal parts of the motor-driven compressor having relatively low corrosion resistance. Additionally, moisture per se causes chemical reaction to occur in the metal parts of the motor-driven compressor thereby to degrade their characteristics.
One of the parts incorporated in an electric motor of the motor-driven compressor that has the lowest corrosion resistance is a permanent magnet. Ferrite magnet and rare earth magnet are mainly used in the electric motor, but they tend to degrade their characteristics in the presence of acid or moisture. Rare earth magnet is more susceptible to acid or moisture than ferrite magnet. Any degraded characteristics of the permanent magnet of the electric motor deteriorates the performance of the motor-driven compressor.
The same problem may occur in conventional refrigerant, any new type refrigerant to be developed in future and lubricating oil contained in refrigerant in the motor-driven compressor, as well as HFO1234yf type refrigerant. Additionally, chemical reaction of moisture with any parts of the motor-driven compressor such as permanent magnet may invite the same problem with the motor-driven compressor.
The present invention is directed to providing a motor-driven compressor which can prevent characteristics degradation of a permanent magnet incorporated in an electric motor.